1. Field of the Invention
This invention is related to soldering electrical components, such as electrical connectors, to substrates, such as printed circuit boards. More particularly, this invention is related to soldering subminiature multiposition electrical connectors to printed circuit boards using surface mount processes, such as laser reflow, hot oil and other surface mount techniques. This invention is specifically related to eliminating contamination of contact surfaces of electrical connectors during soldering operations, including fluxing and flux removal and cleaning operations in general. This invention is also related to subminiature electrical connectors of this type in which connectors of substantially the same design can be used to interconnect printed circuit boards that must be spaced apart by different distances.
2. Description of the Prior Art
The two typical methods of soldering electrical or electronic components, such as electrical connectors, to printed circuit boards are through hole soldering and surface mount soldering. Surface mount soldering offers certain advantages over through hole soldering, primarily the ability to achieve higher component density and therefore smaller overall printed circuit board assembly size. Therefore surface mount soldering is the preferred technique for applying large numbers of components to printed circuit boards having a relatively small available circuit board surface area. Devices such as laptop or notebook or pocket computers, personal digital assistants, portable computer accessories, and cellular telecommunications devices are typical examples of applications in which a large number of components must be soldered to relatively small printed circuit boards.
Electrical connectors for connecting traces on one printed circuit board to another printed circuit board represent one of the relatively larger components employed in such applications. Many electrical connectors are of the through hole type and their use with surface mount applications can either require an additional soldering operation, sometimes even a hand soldering operation, or can restrict the soldering processes to those applicable to hybrid surface mount and through hole boards. Surface mount electrical connectors are, however, available for use on printed circuit boards that use only surface mount devices. It is important that these connectors be as small as possible, both so that the total surface area and volume of the printed circuit board assemblies and subassemblies can be as small as possible and to minimize the length of circuit paths in high speed applications.
Surface mount electrical connectors typically employ a number of electrical contacts mounted in an insulative connector housing. In applications where two printed circuit boards are to the connectable and disconnectable, for example for attaching additional memory and the like, these connectors comprise mating plug and receptacle connector members. Mating terminals or contacts in the receptacle and plug connectors must have mating or contact surfaces for establishing and maintaining electrical continuity with the mating terminal or contact. Typically this contact is maintained by resilient engagement of the mating contacts.
Each of these mating terminals must also include a surface mount solder lead positioned on an exterior surface of the connector housing. Although there are several standard surface mount lead configurations, including gull wing, J-leads and I-leads or butt leads, the conventional surface mount lead used for surface mount electrical connectors includes a section soldered to a surface mount pad on a printed circuit board with this solder section extending parallel to the printed circuit board and substantially at a right angle relative to the terminal or contact. These solder lead sections should also be visible for inspection and therefore clearance is normally provided along the lower edge of the connector housing. These terminals are inserted into cavities in a connector housing from the top or from the bottom with the solder lead section extending parallel to the base of the connector housing. The opening in the housing base through which the contact is inserted must either provide clearance for the contact portion of the terminal or the parallel lead section. For conventional connectors this opening exposes the contact portion of the terminal to the solder process. One common problem encountered with these conventional connectors occurs when solder flux from the circuit board enters the housing cavities and forms a flux film on the mating portion of the terminals. These flux films, may not be completely removed during the washing or cleaning process. Even where "no wash" solder flux is used, there may still be some contamination due to flux residues on the mating contact portions of terminals. These flux residues contaminate the contacts and adversely affect the performance and reliability of the connectors. Even where solder flux and other fluids can be controlled during normal surface mount processes, these problems can also arise during repair of defective solder joints where it is not possible to control the application of solder flux and other fluids to the same extent as during the initial soldering process.
One prior art approach to this problem is to seal the bottom of the connector after the contacts have been inserted. Some have suggested that plugs be inserted into the cavity openings. However, the most common means of flux blockage that has been attempted in the industry is the use of a sealant dispensed into or onto the connector after connector assembly to seal the cavity openings. Application of a sealant after the connector has been assembled is a cumbersome, expensive and undesirable process.
Of course problems with solder, solder flux, contaminants and lead placement are also affected by the need to make the connector package as small as possible. Even though circuit board real estate is generally at a premium, different connectors are needed for different applications in which the spacing of parallel boards is different. In other words different connector heights are needed. For example, one commercially available parallel board to board plug/receptacle connector assembly is available in twelve different heights ranging from 5 mm (0.197 in) to 16 mm (0.630 in). Four plug connectors and three receptacle connectors are required to provide twelve different mating connector assemblies ranging from 5-16 mm in increments of one min. There are applications for connectors with heights ranging from 4 mm (0.158 in) to 25 mm (0.985 in). Furthermore different applications will require connectors with different numbers of positions. For example, the commercially available connector assembly just mentioned is available from forty to two hundred positions, in increments of twenty positions. Since applications for connectors of this type are always changing, the useful life, from conception to obsolescence, of a specific connector with a given height and number of positions, may be quite short. The short life of these connectors places additional constraints on their design due to tooling and other costs. There is a need for relatively simple designs with designed-in flexibility for production of basically similar connectors with different heights and different numbers of positions in order to reduce the cost of each connector. If the connector cost can be reduced and if processes such as washing the printed circuit board assembly after soldering can be eliminated, the installed cost of the connector can be reduced and the cost of the entire product can be reduced.